U.S. President Donald Trump issued a volley of tweets on Sunday night venting anger on some of Washington's closest NATO allies over the United State's trade deficit, following a divisive G7 meeting in Canada.

"Fair trade is now to be called fool trade if it is not reciprocal," said Trump, who flew from Canada to Singapore for a meeting with North Korean leader Kim Jong Un.

"Not fair to the people of America! $800 billion trade deficit," he said. "Why should I, as president of the United State, allow countries to continue to make massive trade surpluses, as they have for decades, while our farmers, workers & taxpayers have such a big and unfair price to pay?"

Trump went on to lambast fellow members of the North Atlantic Treaty Organisation (NATO) for paying disproportionately less than the United States to maintain the Western alliance.

"The U.S. pays close to the entire cost of NATO - protecting many of these same countries that rip us off on trade (they pay only a fraction of the cost - and laugh!)," he tweeted. "The European Union had a $151 billion surplus - should pay much more for military!"

"Germany pays 1 percent (slowly) of GDP towards NATO, while we pay 4 percent of a much larger GDP. Does anybody believe that makes sense?"

"We protect Europe (which is good) at great financial loss, and then get unfairly clobbered on trade. Change is coming!"

Trump also renewed attacks on Canadian Prime Minister Justin Trudeau, who had hosted the G7 meeting in Quebec.

"Justin acts hurt when called out!" the U.S. president said in his latest Tweet. On Saturday, he called the Canadian prime minister "very dishonest and weak."

Trump took aim at an unspecified news release issued by Canada saying, "they made almost 100 bln dollars on trade with u.s. (guess they were bragging and got caught!)."

Trump's supporters also criticised Trudeau.

"(Trudeau) really kind of stabbed us in the back," White House economic adviser Larry Kudlow, who had accompanied Trump to Canada, said on CNN's "State of the Union."

Trade adviser Peter Navarro told "Fox News Sunday" that "there is a special place in hell for any leader that engages in bad faith diplomacy" with Trump.

U.S. President Donald Trump issued a volley of tweets on Sunday night venting anger on some of Washington's closest NATO allies over the United State's trade deficit, following a divisive G7 meeting in Canada.